We have experienced 2 failures on 2 PCBs where the Concerto processor (F28M35H52C1) appears to have an internal short that is pulling a lot of power from an on-board 3.3V regulator. The failure has been intermittent both times, where we have run for several days and multiple power cycles but then upon application of power we have noticed a high current draw, and the 3.3V line is being pulled down to about 2V. Two other boards have been tested and did not experience the failure yet. We are having some difficulty determining the cause of the failure but have collected the following data on the effects:
· All V_DDIO pins on the MCU are tied to a 3.3V, 3A voltage supply. On the 2 failed boards, the 3.3V regulator was current limiting and the 3.3V bus was getting pulled down to about 2V.
· V_DDIO pins 67, 74, 83, 86, and 92 read 30 Ohms to ground on one of the units and 50 Ohms to ground on the 2nd unit.
o The remaining V_DDIO pins do not appear to have been affected.
· There is a direct short from the shorted power supply pins to pin 86 which is a EMU1, JTAG signal.
o There were no external JTAG connections to the board when it failed.
o The JTAG lines are buffered from a connector on the board to the MCU.
· The 1.2V and 1.8V regulators in the part were not affected by the failure and still put out their correct voltage.
Is there a block diagram of the MCU that would show how power is distributed throughout the part or what logic units the listed supply pins are sourcing internally since it appears only a few of the supply pins were affected?
Thank you!
